各位老師和同學(xué)：

　　應王強研究員邀請，國際著(zhù)名地球化學(xué)家和巖石學(xué)家Chris J. Hawkesworth教授訪(fǎng)問(wèn)我所，并將于今天上午做“同位素室學(xué)術(shù)報告”2019年第26次報告。歡迎大家參加并積極參與討論！

　　Topic: The Onset of Plate Tectonics on Earth

　　Speaker: Prof. Chris J. Hawkesworth (Univ. of Bristol)

　　Time: 10:30 AM, October. 8th (Tuesday)

　　Place:

　　Conference Room 108 of Sample Building

　　報告人簡(jiǎn)介:

　　Chris J. Hawkesworth教授是國際著(zhù)名地球化學(xué)家和巖石學(xué)家。他的研究興趣非常廣泛，主要包括同位素地球化學(xué)、大陸地殼形成與演化、沉積和構造過(guò)程的地質(zhì)記錄、大火成巖省和地幔柱、造山帶熱演化以及氣候變化的地球化學(xué)記錄等等，并在這些領(lǐng)域均做出了具有重要國際影響力的突出成果。他已經(jīng)出版學(xué)術(shù)專(zhuān)著(zhù)6本，發(fā)表論文逾316篇，且主要發(fā)表在國際重要刊物上，其中在《Nature》和《Science》上就發(fā)表論文37篇（第一作者11篇），論文引用逾38000次。他先后榮獲英國皇家學(xué)會(huì )院士和蘇格蘭皇家學(xué)會(huì )院士、美國地球物理聯(lián)合會(huì )和歐洲地球化學(xué)協(xié)會(huì )Fellow、倫敦地質(zhì)學(xué)會(huì )Wollaston和Major John Coke獎、英國皇家學(xué)會(huì )Wolfson Merit獎、歐洲地質(zhì)協(xié)會(huì )Robert Wilhelm Bunsen獎、英國礦物學(xué)會(huì )Schlumberger獎、中國科學(xué)院“國際杰出學(xué)者（原愛(ài)因斯坦講座教授）”（2015和2018年）、以及丹麥哥本哈根大學(xué)榮譽(yù)博士學(xué)位等，也曾任《Science》、《EPSL》和《Geology》等刊物編委和英國圣安德魯斯大學(xué)副校長(cháng)等。

　　Abstract:

　　Plate tectonics is a globally linked system of lateral motion of rigid surface plates. Estimates of its onset range from the Hadean to the Neoproterozoic; over three-quarters of Earth history. This contribution considers the spatial and temporal distribution of a range of geological constraints as to when plate tectonics began. It explores ways in which the results of detailed case studies carried out in different locations can be put into a more global context.

　　Tectonic styles, and the degree of seismic anisotropy, are different in different Archaean terranes. Those with dome and basin geometries, associated with vertical tectonics, characterise the Australian Pilbara and southern Africa cratons. They tend to be associated with within-plate magmatism. Linear Archaean orogenic systems with pronounced regional deformation fabrics appear to be characterised by lithosphere of greater seismic anisotropy, as in North America. These in turn tend to be characterised by fluid flux melting in the mantle, as in subduction zones at the present day, and in some areas terrains with stronger regional fabrics are younger than those in which such fabrics are less well developed. Magma types similar to those from recent within-plate and subduction-related settings were generated in different areas at broadly similar times in the period 3.8-2.7 Ga. It may be that subduction took place locally, but that is not necessarily evidence that plate tectonics was active globally.

　　The end of the Archaean is marked by the development of passive margins and of supercontinents, the preservation of major dyke swarms, an increase in the degree of crustal reworking, and a shift in the composition of both juvenile and upper crust from mafic to more intermediate compositions accompanied by an increase in the thickness of the crust at the sites of crust generation. Critically it marks a ~70% reduction in the rates of crustal growth which is attributed to an increase in the rates of crustal recycling. It is argued that these global signals reflect the transition to plate tectonics as a sustainable global tectonic system on Earth.